In reply to tony:
Waterproof printer paper works, when combined with software that allows you to make legal prints of copywrighted works.
Now this may be against copywright, but for personal use.....
Maybe scan in the part of the map, and print onto waterproof paper, or if you have one ofthose all in one print scan copy things, miss out the scan, and copy straight onto the waterproof paper. I am not sure the paper works in a normal photocopier, has to be inkjet (laser may work, not sure)
I have never done this, just an idea.